(1) Field of the Invention
This invention relates to a process for preparing a heterocyclic aromatic amine or an arylamine, which is an important intermediate in pharmaceutical and pesticide applications.
(2) Description of the Related Art
Processes are known wherein a heterocyclic aromatic halide or an aryl halide is allowed to react with an amine to give a heterocyclic aromatic amine or an arylamine, respectively, by using a copper catalyst (see, for example, Dai-yuki Kagaku Organic Chemistry! vol. 16, 52 (1959) published by Asakura Shoten; and Yuki Kagaku Koza Lectures on Organic Chemistry! 3, 66 (1983) published by Maruzen). In the processes using a copper catalyst, the yield of an arylamine or a heterocyclic aromatic amine is low because a salient amount of the catalyst must be used and a high reaction temperature is required. Further, the arylamine or the heterocyclic aromatic amine is difficult to purify from the reaction system because the reaction products are inevitably colored to a large extent.
Recently Stephen L. Buchwald et al have reported a process for synthesizing an arylamine from an aryl halide and an amine compound Angew. Chem. Int. Ed. Engl., 34, No. 12, 1348 (1995!. In this process, an aryl bromide is allowed to react with an amine in the presence of sodium tert-butoxide as a base by using a catalyst comprising a palladium compound having tri-o-tolyl phosphine as a ligand, i.e., bis(dibenzylidene-acetone)-bis(tri-o-tolylphosphine)palladium or dichloro-bis(tri-o-tolylphosphine)palladium. An analogous process has been reported by John F. Hartwig et al in Tetrahedron Letters, vol. 36, No. 21, 3609 (1995).
Further a process has been reported wherein an arylamine is synthesized from an aryl iodide by using a catalyst comprising a palladium compound having tri-o-tolylphosphine as a ligand in J. Org. Chem., 61, 1133 (1996).
In the processes using a palladium compound having tri-o-tolylphosphine as a ligand, especially when an amine compound having a hydrogen atom on the carbon .alpha. to the nitrogen atom is reacted with an aryl halide, a salient amount of bisaryl derivatives are produced each from two molecules of the aryl halide and a salient amount of arene derivatives are produced by dehalogenation, with the result of reduction in the yield of an intended arylamine. Further the amount of the palladium compounds described in the above reports used is large, i.e., 1 to 5% by mole per mole of the aryl halide, and thus the processes are costly.